Attitudes to sex have changed dramatically over the last hundred years. This column presents a model where socialisation – the passing on of norms and ideologies by parents and institutions such as the church or state – is determined by the technological environment in which people live. Contraception has reduced the chance of unwanted pregnancies from premarital sex, and this in turn has changed social attitudes.

The last one hundred years have witnessed a revolution in sexual behaviour. In 1900, only 6% of US women would have engaged in premarital sex by the age of 19, compared to 75% today (see figure 1). Public acceptance of premarital sex has reacted with a lag; in 1968 only 15% of women had a permissive attitude towards the act, despite the fact that about 40% of 19 year-old females had had premarital sex. The number with a permissive attitude had jumped to 45% by 1983, a time when 73% of 19 year olds were sexually experienced.

Figure 1. Premarital sex, attitudes, and practice

Beyond the evolution and acceptance of sexual behaviour over time, there are relevant cross-sectional differences across females. In the US, the odds of a girl having premarital sex decline with family income. For instance, in the bottom decile 70% of girls between the ages of 15 and 19 have had premarital sex versus 47% in the top decile. Similarly, 68% of adolescent girls whose family income lies in the upper quartile would feel "very upset" if they got pregnant, compared to 46% of those whose family income is in the lower quartile.

The consequences for public policy of these observations are important. Higher fractions of women engaging in premarital sex usually bring about more teenage childbearing, even when better contraceptives are available (see Figure 2). Teenage pregnancies have unfortunate consequences for the welfare of children – see for example Hoffman and Maynard (2008). Similarly, the spread of sexually-transmitted diseases, such as HIV/AIDS, is a positive function of the proportion of young adults engaging in sex. As a way to reduce teenage pregnancies and the prevalence of sexually-transmitted diseases, governments have funded programs aimed at promoting abstinence or creating good “social norms.”

The idea

These observations call out for a more thorough understanding of what drives the change in social norms and behaviour and what type of policies will be more effective in improving social welfare. Fortunately, there is a long tradition in economics of studying these issues, going back at least to Gary Becker (1976). After Becker’s pioneering work a literature has developed on modelling the formation of preferences, beliefs, and norms. For instance, Becker and Mulligan (1997), Bisin and Verdier (2001), or Doepke and Zilibotti (2008) have emphasised how parents mould, at a cost of time and money, their children’s preferences. Our work follows this tradition.

The fundamental idea is that young adults act in their own best interest when deciding to engage in premarital sex. They weigh the benefits from the joy of sex against its cost – the possibility of having an out-of-wedlock birth. An out-of-wedlock birth has many potential costs for young women; it may reduce her educational and job opportunities; it may damage her prospects in the marriage market; she may feel shame or stigma. Over time the chance of becoming pregnant – the failure rate – from premarital sex has declined, due to the two facts that contraception has improved, and that more teens are using some method (Figure 2). The cost of engaging in premarital sex has fallen as a result. This leads to the paradoxical situation where, despite the fact that the efficacy of contraception has increased, so has the number of out-of-wedlock births.

The stigma that a young woman incurs from premarital sex may drop over time too. Suppose that parents instil a proscription on premarital sex into their daughters' moral fibres. As the noted sociologist James Coleman (1990, p. 295) nicely put it, “the strategy is to change the self and let the new self decide what is right and what is wrong (for example, by imagining what one's mother would say about a particular action).” Parents do this because they want the best for their daughter. They know that an out-of-wedlock birth will damage their daughter's welfare. As contraception improves, the need for the proscription diminishes and with it the amount of parental indoctrination. The same shift in incentives may also change the moral commands from institutions such as the church and state.

Differences in the costs of an out-of-wedlock birth also explain the cross-sectional observations. The desire for parents and institutions to "socialise" children – pass on norms, customs, and ideologies – will be smaller the less its impact is on a child's future well being. Therefore, there may be little incentive to socialise children at the bottom of the socioeconomic scale because they have nowhere to go in life anyway.

Some quantitative theory

In recent research (Fernández-Villaverde et al. 2010), we explore these mechanisms, both theoretically and quantitatively, and build an overlapping generations model where parents spend effort on socialising their children. The concept of socialising children is operationalised by letting a parent influence his offspring's tastes about an out-of-wedlock birth. Doing so incurs a cost in terms of effort to the parent. After socialisation, some offspring will engage in sex, resulting in a percentage of out-of-wedlock births, and others will not. Of course, when deciding on whether or not to engage in premarital sex, a young teenage girl weighs the joy from sex against the cost of an unwanted pregnancy – the shame incurred and the loss of career or marital prospects.

First, we calibrate the steady state for our model to match some stylised facts for today's US economy. In particular, the model economy is consistent with the observations that more educated women are less likely to engage in premarital sex while they are teenagers – see Figure 3 – and that more educated parents spend more time socialising their children – see Figure 4.

Figure 3. Cross-sectional relationship between the odds of a girl engaging in premarital sex and her educational background, data and model

Figure 4. Cross-sectional relationship between the time spent with a daughter and the mother's educational background, data and model

Second, some transitional dynamics are computed for the situation where society faces a known time path of technological progress in its contraceptive technology. It is demonstrated that the model – see Figure 5 – can replicate the observed rise in premarital sex and out-of-wedlock births due to a fall in the failure rate, and the associated decline in socialisation. If socialisation did not change over the years and stayed at its initial 1900 values, then premarital sex would be much less prevalent than it is today – only around 40% of its current level.

Last, illegitimacy is also costly for institutions such as the church and state, which have typically provided unwed mothers with some form of charity. We briefly consider a Ramsey-style problem where the church and state tries to influence attitudes in order to minimise the number of out-of-wedlock births net of the cost of socialisation. The upshot is that indoctrination by the church and state falls over time as contraception becomes more efficient.

Figure 5. The decline in socialisation (time spent with a daughter) and the rise in out-of-wedlock births, model

Our analysis also connects with the evidence regarding “ethnic capital” documented by Borjas (1992), Fernández and Fogli (2009), and Guiliano (2007). Imagine a young girl who is raised in a society where contraception is not widely available. Her parents socialise her accordingly. Now, suppose that at the start of her teenage years the family immigrates to the US. This teenager should be less promiscuous than an American, because her shame from an out-of-wedlock birth will be greater. If there is any aspect of habit persistence in preferences across the generations within a family line, this effect will carry over to the girl’s own children and grandchildren. Note that the effect will wither away over time, though. The girl will have less incentive to socialise her own daughters against the perils of premarital sex because the need is less in the US, and thus they will feel less shame from an out-of-wedlock birth, and so on.

Lesson learnt

The great sociologist William Ogburn (1964) suggested that a large part of social change was a reaction to technological progress. Our research presents a mechanism where socialisation, by parents and institutions such as the church or state, is determined by the technological environment that people live in. While a simpler model that focused only on technological advances in contraception could generate the rise in premarital sex without an appeal to the socialisation process, it would miss the dramatic changes in sexual norms that history convincingly documents. For example, 69% of all criminal cases in New Haven between 1710 and 1750 were for premarital sex. Such crimes could be punished by fines, public whippings, and jail terms. This begs the question of why such draconian measures were initially adopted and then abandoned by parents, churches and states. An answer is provided here.